In a network, nodes communicate with the network hub during designated time intervals or allocations. The time intervals may be scheduled and assigned to particular nodes. A contended allocation is a time interval having a constrained length outside of the scheduled allocations. The contended allocation is obtained by a node using carrier sense multiple access with collision avoidance (CSMA/CA), for example, for its random access. A contended allocation is typically used for unpredictable or on-demand uplink traffic, such as traffic caused by data rate variations and/or channel impairments. A contended allocation is typically used as an uplink and serves transmissions initiated by a node and corresponding acknowledgments, if any, returned by a network hub or cluster coordinator.
A node uses a backoff counter to determine the start time of a contended allocation. The node sets the backoff counter to some value and then decrements the counter upon detection of certain events. A contended allocation starts when the backoff counter decrements to zero. However, collisions between nodes that attempt to obtain access in the same contended access phases must be resolved without excessive backoffs which would otherwise lead to wasted bandwidth and increased latency.
Nodes using random access methods must also avoid conflicts with scheduled access intervals, beacon frame transmissions, and other pre-allocated time slots. As a result, the node may go through excessive resets of the backoff counter before obtaining a contended allocation. Accordingly, there is a need to resolve collisions between contended allocation intervals and avoid conflicts between contended and scheduled or other non-contended allocation intervals without requiring a node to continually double or reset the backoff counter.